3 files changed, 5 insertions, 3 deletions

diff --git a/Cargo.lock b/Cargo.lock
index ba9a201b9..90c505f40 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -872,6 +872,7 @@ dependencies = [
  "ra_hir 0.1.0",
  "ra_syntax 0.1.0",
  "ra_text_edit 0.1.0",
+ "rustc-hash 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "test_utils 0.1.0",
 ]
 
diff --git a/crates/ra_assists/Cargo.toml b/crates/ra_assists/Cargo.toml
index 434e6656c..50be8d9bc 100644
--- a/crates/ra_assists/Cargo.toml
+++ b/crates/ra_assists/Cargo.toml
@@ -10,6 +10,7 @@ doctest = false
 [dependencies]
 format-buf = "1.0.0"
 join_to_string = "0.1.3"
+rustc-hash = "1.0"
 itertools = "0.8.0"
 
 ra_syntax = { path = "../ra_syntax" }
diff --git a/crates/ra_assists/src/ast_transform.rs b/crates/ra_assists/src/ast_transform.rs
index ace59f290..cbddc50ac 100644
--- a/crates/ra_assists/src/ast_transform.rs
+++ b/crates/ra_assists/src/ast_transform.rs
@@ -1,5 +1,5 @@
 //! `AstTransformer`s are functions that replace nodes in an AST and can be easily combined.
-use std::collections::HashMap;
+use rustc_hash::FxHashMap;
 
 use hir::{db::HirDatabase, InFile, PathResolution};
 use ra_syntax::ast::{self, make, AstNode};
@@ -35,7 +35,7 @@ impl<'a> AstTransform<'a> for NullTransformer {
 
 pub struct SubstituteTypeParams<'a, DB: HirDatabase> {
     db: &'a DB,
-    substs: HashMap<hir::TypeParam, ast::TypeRef>,
+    substs: FxHashMap<hir::TypeParam, ast::TypeRef>,
     previous: Box<dyn AstTransform<'a> + 'a>,
 }
 
@@ -47,7 +47,7 @@ impl<'a, DB: HirDatabase> SubstituteTypeParams<'a, DB> {
     ) -> SubstituteTypeParams<'a, DB> {
         let substs = get_syntactic_substs(impl_block).unwrap_or_default();
         let generic_def: hir::GenericDef = trait_.into();
-        let substs_by_param: HashMap<_, _> = generic_def
+        let substs_by_param: FxHashMap<_, _> = generic_def
             .params(db)
             .into_iter()
             // this is a trait impl, so we need to skip the first type parameter -- this is a bit hacky